design of kompsat-6 polarimetric calibration system

Design of Kompsat-6 Polarimetric Calibration System

Dochul Yang*, Horyung Jeong, Dong Kim, Donghan Lee

S AR Im age , 백두산 Opt ica l Im age , 백두산

• K6 Mission & Characteristics

• K6 Calibration System

• K6 Multi-Polarimetric Calibration Subsystem

• K6 Calibration Equipment Development

K-6 Mission & Characteristics

K6 Mission

Objectives: Expedite provision of the space-borne SAR standard images with sub-meter resolution required for the national demand in GIS (Geographical Information Systems), Ocean & Land management, Disaster monitoring, and ENvironment monitoring

Mission Application: “GOLDEN”

• GIS : Acquisition of independent high resolution images

• Ocean & Land Management : Survey of natural resources

• Disaster & ENvironment Monitoring : Surveillance of large scale disasters and its countermeasure

Expected Launch Date: September, 2020

Life Time: 5 years

K6 Characteristics

SAR Payload

• Space-borne Synthetic Aperture Radar

• X-band radar with an active phased array antenna

• Implemented by four SAR modes

High Resolution A/B Modes : Sliding Spot

Standard Mode : Stripmap

Wide Swath Mode : TOPS

• Electrical steering capability in both azimuth and elevation planes

• Coherent Dual Polarization (HH+HV, VV+VH)

• Quad Polarization & ATI/GMTI as Experimental Modes

Imaging Operation Performance

Observation Mode

• High Resolution-A Mode (Spotlight) : 0.5 m resolution / 5 km swath

• High Resolution-B Mode (Spotlight) : 1 m resolution / 10 km swath

• Standard Mode (Stripmap) : 3 m resolution / 30 km swath

• Wide Swath Mode (TOPS) : 20 m resolution / 100 km swath

Incidence Angle Range

• 20 ~ 55 deg (nominal)

• 55 ~ 60 deg (extended)

Imaging Time

• Continuously 150 sec per orbit

Target Revisit Time

• 53 hours on average

K-6 Calibration System

K6 Cal. System Overview (1/2)

Functions

• Range & Azimuth Antenna Pointing Offset Measurement

• Geometric Range & Azimuth Offset Measurement using Point Target

• Product Coverage Location Error Measurement

• Antenna Pattern Verification

• Absolute Radiometric Calibration Factor Evaluation

• Polarimetric Effects (Channel Imbalance & Cross-Talk) Compensation

• Long-Term & Daily Calibration Image Scheduling

Subsystems

• PCS: Pointing Calibration Subsystem

• GCS: Geometric Calibration Subsystem

• RCS: Radiometric Calibration Subsystem

• MCS: Multi-polarimetric Calibration Subsystem

• CSS: Calibration Scheduling Subsystem

K6 Cal. System Overview (2/2)

Architecture

MCE IRPE CSS

Image Collection

Plan

RCS MCS GCS PCS

Level Product

IRPE

Ground CAL Target ( Amazon , AT, and CR .)

K 6 CE

Download SAR Science

Data (Image + Ancillary) Upload

CMD

Level

Product

Image Collection

Request

ATT & CMD

Time Offset

APLUT

AZCUT [TBD]

CALCO

Channel

Imbalance &

Cross-talk Azimuth & Range

Time Offset

Channel

Imbalance &

Cross-talk

APLUT

AZCUT [TBD]

CALCO

K-6 Multi-Polarimetric Calibration Subsystem

(MCS)

MCS Overview (1/4)

Function

• Compensate polarimetric distortions of SAR antenna

Measure cross-talk & channel imbalance of SAR antenna using images of Amazon rain forest, K6 Active Transponder (AT), and Corner Reflectors (CR)

Provide estimated polarimetric distortion information to K6 SAR Processor

Verify the estimated polarimetric distortion using AT or CR images

Methodologies

• Quad Pol. Calibration

Use three K6 AT (baseline)

Use Amazon rain forest and AT or CR (backup)

• Dual Pol. Calibration

Use three K6 AT and compensate receiving antenna distortions

• Verification Method

Use ATs and/or CR => Scattering Matrix 1 11 1

and 1 00 1

MCS Overview (2/4)

Procedure (1)

• Quad Pol. & three AT method

1) Calculate the peak points around three AT

imaged with quad pol.

2) Estimate antenna polarimetric distortions

(cross-talk and channel imbalance together)

using the ratios between peak points of

different ATs with different scattering matrix

3) Eliminate antenna polarimetric distortions from

point target (AT or CR) images

4) Verify the antenna distortion estimates by

measuring co-pol and cross-pol responses of

AT and/or CR

Extraction of Peak Points from 3AT Quad

Pol. Images

Estimating of Antenna Polarimetric Distortions (X-talk, CI)

Elimination of Antenna Distortions

from Point Target images (AT or CR)

Verification of Antenna Distortions

using AT or CR Cross-talk: 𝛿1 , 𝛿2, 𝛿3, 𝛿4

Channel Imbalance: 𝑓1, 𝑓2

𝑀𝐻𝐻 𝑀𝐻𝑉

𝑀𝑉𝐻 𝑀𝑉𝑉= 𝐴𝑒𝑗𝜑 1 𝛿2

𝛿1 𝑓1

𝑆𝐻𝐻 𝑆𝐻𝑉

𝑆𝑉𝐻 𝑆𝑉𝑉

1 𝛿3

𝛿4 𝑓2

MCS Overview (3/4)

Procedure (2)

• Quad Pol. & DT method

1) Generate covariance matrix of Amazon rain

forest quad pol. images

2) Estimate (u, v, z, w) components in X-talk

matrix using the generated covariance matrix

3) Estimate (α) component in X-talk matrix using

the noise ratio between HV and VH channel

calculated from calm water on image

4) Eliminate X-talk contribution from point targets

(AT or CR) image

5) Estimate Channel Imbalance using the point

targets image

6) Verify the co-pol and cross-pol responses after

eliminating antenna distortions using AT or CR

Covariance Matrix Generation

X-talk Matrix (u, v, z, w ) Estimation

X-talk Matrix (α) Estimation using

Noise Info.

Eliminate X-talk from P.T. Image

Channel Imbalance Estimation

Verification using AT or CR

2 0 0

( ) 0 01

0 0 11

HH

HH

HV

HV

VH

VV

VV

M v w vwk

u vK k

z w

uz u

SM

S

Sz

M

M

X-talk Matrix

MCS Overview (4/4)

Procedure (3)

• Dual Pol. & three AT method

1) Calculate the peak points around three AT

imaged with dual pol.

2) Estimate antenna polarimetric distortions

(cross-talk and receiving channel imbalance

together) using the ratios between peak points

of different ATs with different scattering matrix

3) Eliminate receiving antenna polarimetric

distortions from point target (AT or CR) images

(transmission cross-talk cannot be eliminated)

4) Verify the cross-pol responses using AT or CR

Extraction of Peak Points from 3AT Dual

Pol. Images

Estimation of Antenna Polarimetric

Distortions (X-talk, receiving CI)

Elimination of Receiving Antenna Distortions

from Point Target images (AT or CR)

Verification of cross-pol responses using

AT or CR

Reception Distortion Transmission Distortion

𝑀𝐻𝐻

𝑀𝑉𝐻= 𝐴𝑒𝑗𝜑 1 𝛿2

𝛿1 𝑓𝑆𝐻𝐻 𝑆𝐻𝑉

𝑆𝑉𝐻 𝑆𝑉𝑉

1𝛿3

MCS Simulation: Quad Pol. & 3 AT Method (1)

Schematic Plot

Polarimetric Distortion & Noise Simulation • Cross-talk Range

Amplitude: −30𝑑𝐵 < 𝛿 < −10𝑑𝐵

Phase: 𝟎° < ∠𝜹 < 𝟗𝟎°

• Channel imbalance Range

Amplitude: 0.9 < 𝑓 < 1.1

Phase: −𝟓° < ∠𝒇 < 𝟓°

Azimuth [m]

Range [m]

Satellite

Active Transponder (AT)

Corner reflector (CR)

Calibration Target

Verification Target

AT

AT

• Noise Range

SNR: 𝟔𝟎 𝒅𝑩

MCS Simulation: Quad Pol. & 3 AT Method (2)

Result

• Co-pol & Cross-pol response of CR after compensating estimated distortions

• 5 Simulation results: CI amplitude

After

Calibration

CI amplitude

Less than ±𝟎. 𝟎𝟒𝟕as in criteria

CI amplitude

MCS Simulation: Quad Pol. & 3 AT Method (3)

Result

• 5 Simulation results: CI phase

• 5 Simulation results: CT amplitude

After

Calibration

CI Phase

Less than 𝟓° as in criteria

CI Phase

After

Calibration

CT Amplitude

Less than 𝟑𝟎 dB as in criteria

MCS Simulation: Quad Pol. & DT Method (1)

Schematic Plot

Polarimetric Distortion & Noise Simulation • Cross-talk Range

Amplitude: −30𝑑𝐵 < 𝛿 < −10𝑑𝐵

Phase: 𝟎° < ∠𝜹 < 𝟗𝟎°

• Channel imbalance Range

Amplitude: 0.9 < 𝑓 < 1.1

Phase: −𝟓° < ∠𝒇 < 𝟓°

• Noise Range

SNR: 𝟔𝟎 𝒅𝑩

Noise Ratio between HV and VH channels

𝜎𝑉𝐻/𝜎𝐻𝑉: 1.5

Azimuth [m]

Range [m]

Satellite

Distributed target (DT)

Active Transponder (AT)

AT

Corner reflector (CR)

Calibration Target

Verification Target

MCS Simulation: Quad Pol. & DT Method (2)

Distributed Target

• Azimuth symmetric is satisfied

• Covariance matrix

HH (dB) HV (dB)

VH (dB) VV (dB)

Average: 62.592 dB Average: 55.0425 dB

Average: 55.0424 dB Average: 62.3786 dB

1 0.0121 0.0082 0.5847

0.0121 0.1737 0.1651 0.0091

0.0082 0.1651 0.1751 0.0091

0.5847 0.0091 0.0091 0.9668

MCS Simulation: Quad Pol. & DT Method (3)

Result

• Co-pol & Cross-pol response of CR after compensating estimated distortions

Items Criterias Results

Polarimetry

HH/VV amplitude ratio ≤ 𝟏 ± 𝟎. 𝟎𝟒𝟕 𝟎. 𝟗𝟖𝟑𝟖 ± 𝟎. 𝟎𝟒𝟑𝟑

HH/VV phase difference [deg.] ≤ 𝟓° −𝟎. 𝟐𝟑𝟕𝟓° ± 𝟐. 𝟑𝟓𝟕𝟓°

Cross talk [dB] ≤ −𝟑𝟎 𝐝𝐁 −𝟒𝟎. 𝟓𝟗𝟔𝟕 ± 𝟓. 𝟗𝟏𝟗𝟒 𝐝𝐁

MCS Simulation: Quad Pol. & DT Method (4)

Result

• 100 times Monte-Carlo simulation results: co-pol response of CR

• 100 times Monte-Carlo simulation results: cross-pol response of CR

HH/VV amplitude 0.9838 ±0.0433

HH/VV Phase −0.2375° ± 2.3575°

Cross-Talk -40.5967 ±5.9194 dB

MCS Simulation: Dual Pol. & 3 AT Method (1)

Schematic Plot

Polarimetric Distortion & Noise Simulation • Cross-talk Range

Amplitude: −30𝑑𝐵 < 𝛿1, 𝛿2 < −10𝑑𝐵

Phase: 𝟎° < ∠𝛿1, 𝛿2 < 𝟗𝟎°

Transmission X-talk 𝛿3 ≈ 0

• Channel imbalance Range

Amplitude: 0.9 < 𝑓 < 1.1

Phase: −𝟓° < ∠𝒇 < 𝟓°

Azimuth [m]

Range [m]

Satellite

Active Transponder (AT)

Corner reflector (CR)

Calibration Target

Verification Target

AT

AT

• Noise Range

SNR: 𝟔𝟎 𝒅𝑩

MCS Simulation: Dual Pol. & 3 AT Method (2)

Result

• 5 Simulation results: Cross-talk

After

Calibration

Less than 𝟑𝟎 dB as in criteria

CT Amplitude CT Amplitude

K-6 Calibration Equipment Development

Active Transponder Development (1/2)

Active Transponder Development Strategy

• Comply the requirement assigned by system for radiometric calibration

• Develop H/W considering enhanced payload parameters (compared to K5)

• Develop functions to support radiometric and multi-polarimetric calibration activity

• Consider “experiences and lessons” learned from K5 active transponder operation during development

Functions to support radiometric calibration

• Transfer stable power to satellite continuously during imaging operation

Operates as point target having stable RCS on ground

• Receive and record satellite TX signal versus time accurately

Supports azimuth antenna verification performed by RCS

Functions to support multi-polarimetric calibration

• All polarization (HH+HV+VH+VV) signal transferring

• Precise scattering property of AT are measured

Active Transponder Development (2/2)

Performance Requirements

• RCS Value: 60 dBsm

• RCS Accuracy: 0.2 dB (RF system), 0.4 dB (all AT system)

• Full Polarimetric support

• Recording of azimuth antenna

• Portable (by 2 persons)

• Weather protection, operating temperature (-20 ~50 °C)

Prototype Design of Kompsat-6 AT

Corner Reflector (Mongolia)

KOMPSAT-5 CR (Reuse)

• Number of CR: ST (20), HR (32)

ST (45dBm2)

HR (35dBm2)

200km

THANKS FOR YOUR ATTENTIONS

KOMPSAT-6